From: Simon Riggs <simon@2ndQuadrant.com>
To: Greg Smith <greg@2ndquadrant.com>
Cc: Jignesh Shah <jkshah@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Rob Wultsch <wultsch@gmail.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Group commit and commit delay/siblings
Date: Wed, 08 Dec 2010 19:00:52 +0000
Message-ID: <1291834852.2872.1168.camel@ebony> (raw)
In-Reply-To: <4CFDBDA2.4050705@2ndquadrant.com>
References: <AANLkTik3dr076BMQ6MqCLZZ0x2-qxmQgWoqCR7c0ePoD@mail.gmail.com>
<AANLkTi=fUBnfR7K5uAQZkvaymuVHzUuCpeu4NOtLOMOU@mail.gmail.com>
<4CFC6814.9010002@2ndquadrant.com>
<28624.1291658109@sss.pgh.pa.us>
<AANLkTim7DE99=R6FH=5bD3yTC9t_xjVUvf+e3knbfoyK@mail.gmail.com>
<4CFDBDA2.4050705@2ndquadrant.com>
On Mon, 2010-12-06 at 23:52 -0500, Greg Smith wrote:
> Jignesh Shah wrote:
> > On Tue, Dec 7, 2010 at 1:55 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >
> >> I could have sworn we'd refactored that to something like
> >> bool ThereAreAtLeastNActiveBackends(int n)
> >> which could drop out of the loop as soon as it'd established what we
> >> really need to know...I'd suggest that we just improve the
> >> coding so that we don't scan ProcArray at all when commit_siblings is 0.
> >>
> >> (I do agree with improving the docs to warn people away from assuming
> >> this is a knob to frob mindlessly.)
> >>
> > In that case I propose that we support commit_siblings=0 which is not
> > currently supported. Minimal value for commit_siblings is currently
> > 1. If we support commit_siblings=0 then it should short-circuit that
> > function call which is often what I do in my tests with commit_delay.
> >
>
> Everybody should be happy now: attached patch refactors the code to
> exit as soon as the siblings count is exceeded, short-circuits with no
> scanning of ProcArray if the minimum is 0, and allows setting the
> siblings to 0 to enable that shortcut:
Minor patch, no downsides. Docs checked. Committed.
--
Simon Riggs http://www.2ndQuadrant.com/books/
PostgreSQL Development, 24x7 Support, Training and Services
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To: pgsql-performance@postgresql.org
Cc: simon@2ndQuadrant.com, greg@2ndquadrant.com, jkshah@gmail.com, tgl@sss.pgh.pa.us, wultsch@gmail.com
Subject: Re: Group commit and commit delay/siblings
In-Reply-To: <1291834852.2872.1168.camel@ebony>
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